The invention relates to a trailer coupling for motor vehicles, comprising a bearing part arranged so as to be fixed on the vehicle, a ball neck which can be moved in relation to the bearing part between an operative position and a rest position and which is mounted on the bearing part by means of a bearing head so as to be at least rotatable, a ball neck fixing means with form locking elements which can be transferred due to relative movement from a fixing position, in which the bearing head is secured relative to the bearing part in a form locking manner, into a release position, in which the bearing head can be moved in relation to the bearing part, and vice versa and a mechanical positioning device, with which the relative movement of the form locking elements can be brought about in order to reach the fixing position and the release position.
The solutions known thus far are either mechanically complicated or not the best in all the possible operating states with respect to being able to achieve a secure locking.
The object underlying the invention is, therefore, to achieve as reliable a safety functioning as possible with a simple mechanical construction, in particular, of the ball neck fixing means.
This object is accomplished in accordance with the invention, in a trailer coupling of the type described at the outset, in that form locking elements are arranged on the bearing part and form locking elements are arranged on the bearing head, that the bearing head can be moved relative to the bearing part in a direction transverse to a pivoting direction in order to move the form locking elements between the fixing position and the release position, that the positioning device can be brought into a fixing position, in which it positions the bearing head in such a manner that the form locking elements are in the fixing position, and can be brought into a release position, in which it positions the bearing head in such a manner that the form locking elements are in the release position, that the positioning device can be brought from the fixing position into the release position by means of an actuation and that the positioning device has a force storing means which generates in the release position a restoring force which acts in the non-actuated state of the positioning device in the direction of a transfer into the fixing position so that the positioning device transfers the form locking elements in the operative position and the rest position automatically from the release position into the fixing position.
The advantage of the inventive solution is to be seen in the fact that due to the displacement of the bearing head a simple possibility exists of moving the form locking elements back and forth between the release position and the fixing position and that, on the other hand, it is possible via the positioning device with the force storing means for the positioning device to transfer the form locking elements automatically from the release position into the fixing position so that the trailer coupling, in the operative position and in the rest position, always transfers automatically from the release position into the fixing position.
In principle, it would be conceivable to allow the restoring force of the force storing means to be constantly active.
One particularly advantageous solution provides, however, for the restoring force of the force storing means to be activatable due to transfer of the positioning device from the fixing position into the release position.
In principle, it would be possible to realize the interaction between the positioning device and the bearing head in such a manner that the positioning device acts on the bearing head merely in the direction of the fixing position and releases it for the transfer into the release position.
For reasons of as reliable a functioning as possible with as little error susceptibility as possible it is, however, advantageous when the positioning device moves the bearing head back and forth between the fixing position and the release position in an automatically controlled manner.
In order for the positioning device not to leave the fixing position when this has been reached, it is preferably provided for the positioning device to have a mechanism which automatically maintains a stable position in the fixing position. As a result of a positioning device of such a design, it is possible to reach the fixing position reliably, on the one hand, and, on the other hand, to prevent the positioning device from leaving the fixing position again.
In this respect, it is even better when the mechanism is self locking in the fixing position against any movement in the direction of the release position so that an even greater functional reliability is ensured.
With respect to the design of the mechanism, the most varied of solutions are conceivable.
It would, for example, be conceivable to design the mechanism as a wheel gear.
A particularly simple solution from a constructional point of view provides, however, for the mechanism to be a lever mechanism.
With respect to the design of the force storing means, no further details have been given in conjunction with the preceding explanations concerning the individual embodiments.
It would, for example, be conceivable to design the force storing means as an electrically acting force storing means, for example, as a magnet or also as a pneumatic force storing means.
A particularly robust and simple solution does, however, provide for the force storing means to be a mechanical force storing means.
The force storing means may be realized in a particularly simple manner from a constructional point of view as a spring force storing means.
With respect to the design of the force storing means in conjunction with the fixing position and the release position, the most varied of possibilities are conceivable.
It would, for example, be conceivable to use the force storing means such that this does not generate any more force in the fixing position.
It is, however, particularly favorable when the force storing means is in a first tensioned state in the fixing position and in a second tensioned state in the release position so that the force storing means is still effective with a force even in the fixing position.
Such a force is of advantage in many cases. For example, it is of advantage so that it can be ensured that the positioning device transfers into the fixing position with the greatest possible functional reliability and does not not reach the fixing position on account of mechanical restraints.
In this respect, it is particularly advantageous when the mechanism, in the non-actuated state of the positioning device, transfers automatically into the stable position due to the action of the force storing means so that the tensioned state of the force storing means in the fixing position can be utilized to maintain the stable position of the mechanism.
With respect to the design of the mechanism, the most varied of possibilities are conceivable. For example, the mechanism could act completely independently of the force storing means and serve merely to achieve the stable position and, where applicable, the self-locking.
It is even more advantageous when the mechanism is a force transfer mechanism for the force storing means so that the force storing means is integrated into the mechanism which thus also serves at the same time to transfer the forces of the force storing means in addition to achieving the stable position.
In order to obtain as advantageous an effect as possible of the forces of the force storing means, it is preferably provided for the force transfer mechanism to be designed as a force transmission mechanism and thus not to transfer the force generated by the force storing means in the same ratio but rather to effect a force amplification at least in some of the possible positions.
A particularly favorable type of force transmission provides for the force transmission mechanism to amplify the force generated in the respective position by the force storing means to a lesser extent in the release position than in the fixing position.
In order to have as large a force as possible available for reaching the fixing position, it is preferably provided for the force transmission mechanism to have the greatest amplification for the force of the force storing means in its positions located close to the fixing position.
The force transfer mechanism may be designed in the most varied of ways.
For example, it would be conceivable to design the force transfer mechanism as a gear.
A particularly favorable solution provides for the force transfer mechanism to be an elbow lever mechanism.
In order to have, on the one hand, forces which are as large as possible available in the fixing position and, on the other hand, to achieve as stable a position as possible, it is preferably provided for the elbow lever mechanism to be designed such that it is close to its dead-center position in the fixing position.
With respect to the action of the positioning device in the fixing position, no further details have so far been given.
In principle, it would be conceivable to design the positioning device such that it positions the form locking elements and the bearing head in the fixing position so as to be free from any force acting on them.
One particularly favorable solution does, however, provide for the positioning device to have a tensioning position as fixing position, in which the positioning device generates a force which contributes to a tensioning force acting on the bearing head.
Such a tensioning force may preferably be used in order to position the bearing head in the fixing position free from play and, therefore, to improve the functional reliability of the trailer coupling, in particular, with respect to the permanent load stability of the trailer coupling.
Such a force may be generated in the positioning device, for example, by means of the force storing means already present.
It is, however, particularly advantageous when the positioning device comprises a tensioning force storing means which generates the force contributing to the tensioning force.
Such a tensioning force storing means is preferably independent of the force storing means for the restoring force so that the stable position of the positioning device can be reached with the restoring force and then the force contributing to the tensioning force can be generated by the tensioning force storing means.
Such a tensioning force storing means is preferably designed as a mechanical tensioning force storing means, in particular, as a spring force storing means.
A particularly advantageous solution provides for the tensioning force storing means to be activatable during the transfer of the positioning device into the tensioning position so that the tensioning force storing means need not constantly be activated but rather is active only in positions close to the tensioning position.
A particularly favorable solution provides for the tensioning force storing means to be active between the tensioning position and a blocking position of the positioning device.
Furthermore, it is favorable when the tensioning force storing means is inactive between the blocking position and the release position.
A particularly advantageous solution provides for the tensioning force storing means to be activatable by the transfer from the blocking position into the tensioning position.
A particularly simple form of the activation of the tensioning force storing means provides for the tensioning force storing means to be activatable by the force storing means. Such an activation may be brought about, in particular, due to the fact that the force storing means transfers the positioning device into the tensioning position and during this transfer activates the tensioning force storing means at the same time.
A particularly advantageous solution from a constructional point of view provides for the tensioning force storing means to be integrated into the mechanism of the positioning device.
This may be realized particularly favorably when the tensioning force storing means is integrated into the force transmission mechanism. In the most advantageous case, the tensioning force storing means is integrated into a lever of the force transmission mechanism designed as a lever mechanism.
In conjunction with the preceding description of the individual embodiments of the inventive solution, no details have been given as to how the positioning device is intended to be actuatable.
For example, it would be conceivable to carry out a direct actuation of the positioning device.
A particularly favorable solution provides, however, for the positioning device to be actuatable by a triggering device, with which primarily a triggering of the positioning device can be achieved with transfer thereof from the fixing position into the release position.
In this respect, it is particularly favorable when the mechanism of the positioning device can be moved into the release position with the triggering device contrary to the action of the force storing means so that the triggering device creates a suitable possibility for transferring the positioning device from the fixing position or tensioning position into the release position.
In order to facilitate the transfer of the positioning device into the release position, it is preferably provided for the triggering device to act with a force amplifying gear on the positioning device so that, as a result, the forces acting in the positioning device, in particular, the force of the force storing means can be overcome more easily.
A particularly favorable solution provides for the triggering device to act on the positioning device with a cam gear.
Furthermore, it is preferably provided for the self locking of the positioning device to be terminated with the triggering device so that the triggering device serves an additional purpose.
In order to provide additional safety, it is preferably provided for the positioning device to be securable in the fixing position or tensioning position with the triggering device so that the triggering device can serve not only for the transfer from the fixing position into the release position but, at the same time, undertakes an additional securing function for the positioning device.
With respect to the actuation of the triggering device, the most varied of possibilities are conceivable. One advantageous solution, for example, provides for the triggering device to be actuatable manually.
In order to decouple such a manual actuation of the triggering device from the elements interacting directly with the positioning device, it is preferably provided for the triggering device to be actuatable manually via a free-moving element acting on an adjusting element.
Such an adjusting element of the triggering device serves the purpose of actuating the positioning device while the free-moving element can be moved in a free-moving manner in relation to the adjusting element so that, for example, the free-moving element can return to its initial position after actuation while the adjusting element remains in accordance with the position of the positioning device and, for example, does not return again to the initial position until the positioning device transfers into the fixing position or tensioning position.
Alternatively or in addition to the manual actuation of the triggering device, a particularly advantageous embodiment provides for the triggering device to be actuatable via an electric triggering drive.
Such an electrically driven triggering drive has the advantage that with it the operation of the inventive trailer coupling, in particular, the triggering can be designed in an operatively friendly manner and, in particular, it is also possible to integrate electrically monitored safety functions, in addition.
The electric triggering drive may be realized in the most varied of way.
For example, it would be conceivable to realize the electric triggering drive by means of an electrically operable triggering magnet drive.
A particularly efficient solution saving, in particular, on current provides for the electric triggering drive to comprise a drive motor and an electrically controllable coupling.
In this respect, the use of an electric drive motor with a reduction gear is particularly advantageous since, as a result, adequately large forces can be generated with low electrical force and, in addition, the controllable coupling creates the possibility of decoupling the drive motor again.
The electrically controllable coupling can be controllable in the most varied of ways.
For example, it would be conceivable to use a coupling which can be switched back and forth by means of electrical actuation between a released and an engaged state.
A particularly favorable solution provides, however, for the electrically controllable coupling to be designed as a coupling released in the state without current. This design of the coupling has the great advantage that the coupling is always released during a power outage and, therefore, a connection between the drive motor and the triggering device is interrupted so that the triggering device always transfers into the non-actuated state during a power outage and, therefore, the trailer coupling can always transfer automatically into its secure position in an inventive manner.
This solution is a great advantage with respect to the functional reliability of the inventive trailer coupling since, as a result, it is ensured even during a power outage that the trailer coupling transfers automatically into its secured state, i.e., into its fixing position or tensioning position without additional measures being required.
With respect to the actuation of the triggering device, the most varied of possibilities are conceivable. For example, it would be conceivable to release the coupling when the triggering device or the positioning device has reached a certain position, wherein this position can, for example, be detected by a sensor.
A particularly reliable solution provides, however, for the electric triggering device to have a triggering control which closes the electrically controllable coupling during a predetermined triggering period following a starting signal and subsequently releases it.
This focusing of the activation of the electrically controllable coupling on a predetermined triggering period signifies an additional, advantageous feature which is relevant with respect to safety since, as a result, a release of the coupling always takes place irrespective of the functioning of the triggering device and the positioning device and, therefore, it is ensured that even when the positioning device or the triggering device does not function in the prescribed manner and, therefore, the position to be detected by the sensor also cannot be reached, for example, the actuation of the triggering device is terminated in any case due to the release of the coupling following the predetermined triggering period.
In this respect, the drive motor of the electric triggering drive is preferably activated in accordance with the coupling during the triggering period.
With respect to the type of action of the positioning device on the bearing head, no further details have so far been given. It would, for example, be conceivable for the positioning device to act directly on the bearing head.
A particularly favorable solution provides for the positioning device to act on the bearing head via a coupling device. Such a coupling device allows mechanical action on the bearing head in a particularly advantageous manner.
With respect to the design of the coupling device, the most varied of possibilities are thereby conceivable.
One advantageous type of design for the coupling device provides for this to comprise a movable bearing pin, on which the bearing head is rotatably mounted and via which the bearing head can be moved from the fixing position into the release position and vice versa. In this respect, the bearing pin could be movable relative to the bearing part transversely or at an angle to its axial direction. It is, however, preferably movable relative to the bearing part in its axial direction.
The provision of a bearing pin for the mounting of the bearing head and, at the same time, for the movement of the bearing head is particularly advantageous from a constructional point of view since the forces required for the positioning of the bearing head may be applied to it in a particularly simple manner via this bearing pin and, in particular, forces acting asymmetrically on the bearing head can be avoided.
In this respect, it is particularly advantageous when the bearing head is movable by means of the movable bearing pin in the direction of a first bearing side wall of the bearing part which bears the form locking elements arranged on the bearing part.
As a result, it is possible in a simple manner to bring the form locking elements into engagement with one another via the bearing pin.
Furthermore, it is favorable when the bearing pin is mounted in the first bearing side wall and in a second bearing side wall of the bearing part arranged at a distance from it and when the bearing head of the bearing neck is arranged between the bearing side walls.
With respect to the location of the action on the bearing pin, no further details have so far been given.
One particularly favorable embodiment provides for the bearing pin to be acted upon from a side of a bearing side wall of the bearing part facing away from the bearing head.
It is particularly favorable when the action on the bearing pin is brought about from the side of the bearing side wall bearing the form locking elements arranged on the bearing part which faces away from the bearing head.
A particularly advantageous solution provides for the coupling device to comprise a reversing lever which is coupled to the bearing pin so that a simple actuation of the bearing pin can be realized via this reversing lever.
In this respect, it is particularly favorable when the reversing lever is arranged on a side of one of the bearing side walls, preferably the first bearing side wall which is located opposite the bearing head.
With respect to an additional securing of the bearing head in the fixing position, no further details have been given in conjunction with the preceding explanations concerning the individual embodiments.
One particularly advantageous embodiment, for example, provides for the bearing head to be blocked by a blocking device against any movement from the fixing position in the direction of the release position and, therefore, an additional securing against any release of the ball neck fixing means to be present.
This blocking device can, in principle, be arranged at the most varied of locations.
In order to be able to absorb the forces acting on the blocking device from the bearing head as advantageously as possible, it is preferably provided for the blocking device to be supported on the bearing part.
In this respect, it is particularly favorable when the blocking device is supported on one of the bearing side walls of the bearing part, preferably on the side wall which bears the form locking elements arranged on the bearing part.
With respect to the actuation of the blocking device, no further details have so far been given.
It would, for example, be conceivable to actuate the blocking device either itself and independently of the positioning device or also, for example, to actuate the blocking device via the positioning device.
It is, however, particularly advantageous when the blocking device can be actuated by the triggering device.
In this respect, the blocking device is preferably coupled mechanically to the triggering device with respect to its functioning so that the transfer of the positioning device from the fixing position into the release position leads to a release of the blocking device coupled mechanically thereto.
In this respect, it is particularly advantageous when the blocking device can be actuated with the triggering device in a defined synchronization in relation to the actuation of the positioning device so that the functioning of the positioning device may be definitively adjusted to the operation of the blocking device and, therefore, a reliable and secure functioning of the trailer coupling can be achieved.
In this respect, it is particularly favorable when the triggering device terminates the effect of the blocking device during the transfer from the fixing position into the release position before the positioning device begins to bring the form locking elements out of engagement.
Furthermore, it is advantageous when the triggering device, during the transfer from the release position into the fixing position, first causes the positioning device to bring the form locking elements into engagement and then causes the blocking device to become active.
With respect to the design of the blocking device, no further details have so far been given. One particularly advantageous embodiment, for example, provides for the blocking device to be designed to be self-readjusting, i.e., for the blocking device not only to block any movement of the bearing head beyond a specific, predetermined position but also, for example, to always follow the position of the bearing head when wear and tear occurs to the extent that this position is adjusted when the fixing position or tensioning position is taken up or also during the course of the fixing position or tensioning position.
Therefore, the blocking device also follows, for example, the position of the bearing head which is adjusted, for example, in the case of wear and tear in the fixing position or tensioning position once taken up and so the readjustment is not only effected when the respective fixing position or tensioning position is taken up but rather the blocking device also acts in a self-readjusting manner in the position once taken up and maintains the respective resulting maximum displacement in the direction of any taking up of the fixing position or the tensioning position.
It is even better when the blocking device not only acts in a self-readjusting manner but acts on the bearing part in its active position with a force contributing to the tensioning force so that the blocking device can also be used at the same time for contributing to the tensioning force.
For this purpose, the blocking device is preferably provided with a force storing means, in particular a mechanical force storing means, such as, for example, a spring force storing means.
The blocking device can, for example, be designed such that it acts directly on the bearing member with a blocking wedge.
For example, it is conceivable to have a blocking wedge supported on the bearing part acting directly on the bearing member.
Such a blocking wedge could be provided, for example, between the bearing member and a bearing side wall.
A particularly favorable arrangement of the blocking device does, however, provide for this to act on the coupling device.
This arrangement of the blocking device makes it possible to arrange it on a side of a bearing side wall of the bearing part facing away from the bearing head.
Such a blocking device is preferably designed such that it comprises a blocking member which interacts with the coupling device and the bearing part.
In this respect, the blocking member is preferably arranged such that it is supported on the bearing side wall bearing the form locking elements arranged on the bearing part.
With respect to the arrangement of the blocking device relative to the positioning device, no further details have so far been given. One advantageous solution provides, on account of their functional interaction, for the blocking device and the positioning device to be arranged on the same side of the bearing part.
Furthermore, a mechanical interaction of the blocking device and the triggering device is facilitated when the blocking device and the triggering device are arranged on the same side of the bearing part.
With respect to the arrangement of the form locking elements on the bearing head, no further details have so far been given. The form locking elements arranged on the bearing head could, in principle, be arranged on all sides of the bearing head.
It is particularly advantageous when the bearing head has a bearing bore which extends at an angle to the horizontal in the state mounted on the vehicle and when the form locking elements are arranged on the side of the bearing head, on which the bearing bore extends closer to the roadway than on the other.
This solution has the advantage that in this area the bearing head can have a greater radial extension in relation to the bearing bore and, therefore, it is possible to arrange the form locking elements in a more stable manner and with a greater radius in relation to the bearing bore and, therefore, to provide a more rigid connection to the bearing part.
Furthermore, in the case of a bearing pin extending at an angle to the horizontal the bearing pin is mounted on the bearing part, preferably on a bearing side wall thereof, at least on its side closest to the roadway.
In the case where the bearing pin is mounted on two bearing side walls, the form locking elements are preferably arranged on the bearing side wall which mounts the bearing pin in its end area located closest to the roadway.
With respect to the arrangement of the form locking elements themselves, the most varied of solution possibilities are conceivable. For example, the form locking elements could be arranged so as to be movable.
With a view to as simple a constructional solution as possible and a mounting which is as free from play as possible, the form locking elements on the bearing part are preferably arranged so as to be stationary.
Furthermore, the form locking elements on the bearing head are also preferably arranged so as to be stationary.
Such a stationary arrangement is to be understood such that the form locking elements are arranged relative to the bearing part or relative to the bearing head so as to be unmovable, i.e., connected rigidly to it.
With respect to the type of interaction of the form locking elements in the operative position and the rest position, no further details have so far been given.
It is particularly advantageous when, in the operative position, one part of the form locking elements located in fixing position is in engagement and another part is not.
Furthermore, it is preferably provided for one part of the form locking elements located in fixing position to be in engagement in the rest position and another part not.
This solution has the advantage that the angular distance between the rest position and the operative position need not be designed in accordance with possible rotational symmetries, i.e., for example, a two-fold or three-fold or four-fold symmetry of the angular distance itself or a multiple thereof would define the possible angular distance between operative position and rest position, but rather that the angular distance can be determined irrespective of the number of form locking elements used.
One advantageous solution provides for at least one first form locking element to be arranged on the bearing part or on the bearing head which is in engagement with a form locking element on the respectively other part only in the operative position and for at least one second form locking element to be arranged on the bearing part or on the bearing head which is in engagement with a form locking element on the respectively other part only in the rest position.
This means that two groups of form locking elements are provided on one of the two parts, wherein the one group is provided for the fixing of the operative position and the other group for the fixing of the rest position while the form locking elements on the other part can be designed such that they are all respectively in engagement either with the one group or with the other group.
In order to bring about a fixing of the bearing head relative to the bearing part which is as free from play as possible, it is preferably provided for at least one form locking element of a pair of form locking elements which are in engagement to have a surface which extends at an angle to a direction of movement of the bearing head and can be abutted on the other form locking element of the pair of form locking elements in a tensioning position so that a tensioning between the form locking elements and, therefore, a fixing of the form locking elements relative to one another which is free from play is possible via this surface extending at an angle.
In this respect, it is preferably provided, in the operative position, for the at least one pair of form locking elements which are in engagement to be acted upon in the tensioning position with a tensioning force in an insertion direction in order to fix the bearing head on the bearing part free from play.
The same measures may, however, also be provided in the rest position in order to achieve a fixing which is free from play in this position.
In order to bring about a fixing which is free from play and as precise as possible, it is preferably provided, in the operative position and/or the rest position, for at least two pairs of form locking elements to be brought into the tensioning position and acted upon with the tensioning force.
It is even more advantageous when, in the operative position and/or the rest position, at least three pairs of form locking elements can be brought into the tensioning position and acted upon with the tensioning force.
The provision of at least three pairs of form locking elements has the great advantage that, as a result, a stable support of the bearing head relative to the bearing part can be realized in the form of a tripod.
The support of the bearing head is particularly stable and free from play when this is supported on the bearing part essentially via the pairs of form locking elements in the operative position and in the tensioning position of the pairs of form locking elements, i.e., no other additional support of the bearing head is brought about and, therefore, solely the pairs of form locking elements are active.
Furthermore, it is particularly advantageous when the position of the bearing head is determined relative to the bearing part essentially via the pairs of form locking elements in the operative position and in the tensioning position of the pairs of form locking elements, wherein any overdetermination by the bearing pin is, in particular, avoided which has therefore to be provided with sufficient clearance.
This exclusive securing of the bearing head relative to the bearing part via the pairs of form locking elements improves the freedom from play and precision of the positioning of the bearing head.
The same preferably applies for the rest position, as well.
In order to prevent the ball neck, during pivoting from the operative position into the rest position, from remaining in a position which does not correspond to either of the two positions and an apparent fixing from taking place in this position, it is preferably provided for the ball neck fixing means to be designed such that the form locking elements can be brought into form locking engagement only in the operative position and the rest position. This solution has the advantage that, as a result, any apparent fixing in an intermediate position can be prevented and, therefore, it is ensured that the inventive trailer coupling has the possibility of transferring from the release position into the fixing position or tensioning position only in the operative position and only in the rest position.
This may preferably be realized in that the ball neck fixing means comprises guide elements which prevent any engagement of the form locking elements in intermediate positions between the operative position and the rest position.
With respect to the possibilities of initiating the rotary movement of the bearing head in order to move the ball neck from the operative position into the rest position or vice versa, the most varied of possibilities are conceivable.
For example, it would be conceivable to initiate the rotary movement via the bearing bolt.
It is, however, particularly advantageous within the scope of the inventive solution when the bearing head is arranged on the bearing pin so as to be freely rotatable.
This makes it possible, for example, to provide all the possible, different types of pivoting of the bearing head relative to the bearing part.
In this respect, one advantageous solution provides for the ball neck to be pivotable manually.
In this case, the bearing head has to be moved only from the fixing position or tensioning position into the release position and, in this position, a manual pivoting is possible on account of the freely rotatable mounting of the bearing head.
Alternatively thereto, one advantageous solution provides for an electrically controllable pivot drive to be provided for the ball neck.
This electrically controllable pivot drive allows a more convenient operation of the trailer coupling and, in addition, such an electrically controllable pivot drive offers the possibility of realizing additional advantageous safety functions via an electrical control.
A particularly advantageous solution provides for the pivot drive to have an electric drive motor.
In this respect, it is preferably provided for the pivot drive to comprise a releasable coupling which allows a manual pivoting of the back neck when the pivot drive fails.
Such a releasable coupling has the great advantage that even with provision of an electric drive motor and failure of the electrics it is still possible to move the ball neck out of every intermediate position either into the operative position or into the rest position.
Such a releasable coupling could, for example, also be a coupling which is automatically released in the case of a power outage.
It is, however, particularly advantageous when the releasable coupling is a slip coupling which is configured such that its triggering moment can be reached when the ball neck is acted upon manually so that when the electric drive fails the pivoting of the ball neck out of every intermediate position into the operative position or the rest position can be realized manually.
Additional features and advantages are the subject matter of the following description as well as the drawings illustrating two embodiments.